Medical device for sensing cardiac function

A wearable medical device for determining whether a patient is experiencing a cardiac event using electrocardiogram (ECG) templates includes a plurality of ECG electrodes and a medical device controller. The medical device controller includes a memory, a baseline generator, a cardiac event detector, and a mode selector. The baseline generator is configured to record a baseline ECG signal, generate one or more ECG templates, and store the one or more ECG templates in the memory. The cardiac event detector is configured to select an ECG template and compare a current ECG signal with the selected ECG template to determine whether the patient is experiencing a cardiac arrhythmia. The mode selector is configured to identify whether any ECG templates are stored in the memory, determine whether a new ECG template is needed, and, upon determining that a new ECG template is needed, enter a baselining mode by activating the baseline generator.